1. Field of the Invention
This invention relates to an expansion joint for constructing concrete structures which, when in use, is disposed between a pair of formworks, which are used when a concrete placement is performed.
2. Description of the Prior Art
In general, when a concrete structure comparatively long in the horizontal direction such as, for example, a bank protection wall, is to be constructed, the constructing portion of the concrete is slightly spaced apart (to form joints) in order to absorb expansion and contraction of the concrete.
The work for constructing such structure having an expansion joint is carried out by setting up a formwork and placing concrete in the formwork, removing the concrete from the formwork after the concrete is cured, attaching an expansible joint material such as a polyethylene foam to a surface thereof, and then setting up the next formwork and placing more concrete therein. When this method is adopted, it is naturally unavoidable that water leaks from the joint. Therefore, various methods for preventing leakage of water have been employed as collectively shown in FIGS. 2A, 2B, 2C and 2D.
That is, FIGS. 2A to 2D are partly sectional views, each schematically showing a portion of a concrete wall and more particularly a cross sectional view in its width direction. In FIGS. 2A to 2D, a joint formed at the portion between concrete bodies A and B extending in the horizontal direction is filled with a polyethylene foam 1 for filling a gap.
And in order to present leakage of water from occurring in the width direction through the joint, various methods are employed for the portion between concrete bodies A and B such as a method for embedding an extensible water stopping plate 2 (FIG. 2A) or 2a (FIG. 2B) extending in the vertical direction to block the joint, a method for interposing a water swelling rubber 3 (FIG. 2C), filling a elastic sealing material 4 (FIG. 2D) to each wall surface, or a method for combining these methods.
In such conventional working method as mentioned above, concrete is removed from a formwork after the concrete is cured, a joint is formed, a water stopping plate is attached, and thereafter the next formwork is set up. Accordingly, it has the disadvantage that much time and labor are required for working, concrete cannot be placed continuously, and working time is long in general.
When reviewing the above-mentioned individual methods, the water stopping method using the water stopping plate 2 or 2a has such problems as that since a single water stopping plate must be placed on the first and second concrete bodies, the setting up of the form-work is very troublesome and the time required for construction is long. Moreover, regarding the water stopping, since a gap is generated between the water stopping plate 2 or 2a and the concrete body A or B, leakage of water is unavoidable. Therefore, in recent years, there was developed a water stopping plate, a part of which is formed of a water swelling rubber in order to completely stop the water leakage. However, this case again is not successful in simplifying the constructing method.
In the method using the water swelling rubber 3, a water swelling rubber may be simply attached to the first placing concrete body and the constructing method is somewhat simplified. However, simple use of the water swelling rubber is not enough for expecting a complete water stop caused by the above-mentioned expansion. In order to obtain a more complete water stop, a larger water swelling rubber compared with the joint width must be used and this gives rise to another problem in respect of cost.
Furthermore, the method using the elastic sealing material 4 has such problems as that the attaching surface is easily peeled caused by repeated expansion and contraction and durability, and therefore leakage of water is unavoidable.